These 10 Sickening Calling Cards Left By Serial Killers Will Send Shivers Down Your Spine...

However scary, serial killers can be a fascinating topic. Many of them throughout history have left some sort of a calling card or signature because they want the world to recognize them for their work.

Here are some of the most interesting signatures from #serialkillers throughout history, and some backstories on each.

10. Dennis Rader: BTK

In his letters to police and media, #DennisRader used the three letters from his killer name, the BTK Strangler; bind, torture, and kill.

The letters were arranged in such a way that they looked like a person, with the "K" turned sideways at the bottom of the stack, and the 'B' on top, turned sideways. He also placed two dots in the 'B' to make it look like a pair of breasts. The detectives did a very good job keeping the signature secret for over 30 years, even in the years that Rader went silent and stopped killing. Or at least they think he stopped. Even #BTK himself didn't let anyone know his signature outside of the authorities, probably for fear someone would copy his work. KAKE news aired a copy of the signature after Rader had been charged with 10 murders between 1974 and 1991.

You can see more on Rader by watching the 2006 film, NBC News Presents: BTK Confessions. Or, believe it or not, his daughter has a book coming out that you can pre-order.

9. Beer Man

Ravindra Kantrole decided the best way of leaving his mark was to leave a beer can beside each victim. All the victims were poor, living on the street, and some were drug addicts because, according to him, they attracted less attention, but all were either stabbed or clubbed to death. Ironically, he was caught while he was getting some food that was being handed out in Mumbai. He claimed he would beat his victims first, as he loved seeing the blood, then would finish off the job by stabbing them. In the end, he got a life sentence, being originally charged for 7 beer can murders. Why he chose a #beer can may forever remain a mystery.

8. Texas Eyeball Killer

In 1991, three prostitutes were murdered in Dallas, Texas. It wasn't long before hairs found at one of the crime scenes matched Charles Albright, so he was convicted and sentenced to life in prison. He was only charged with that murder, but was suspected of the other two. This guy's signature was pretty gruesome; as he took his victim's eyes as a souvenir. He insists that he is innocent to this day. However, the drawings of #eyeballs in his cell seem to suggest otherwise.

For more information on Albright, check out the documentary, Charles Albright: The Texas Eyeball Killer.

7. Boston Strangler

This one is about a serial killer who murdered 13 women, mostly elderly, but was never officially “found” or convicted. Albert DeSalvo was the man they had in prison who confessed to all the murders, but they were never able to prove that he was the killer. After serving some time for breaking and entering, DeSalvo attacked and molested a woman, but didn't kill her. She identified him and he went to prison. As for the murders, each one was found strangled with their own underwear, stockings, or scarves. One had a cord around her neck in her bathroom, but all of the things used to strangle the women were tied in a bow around their necks.

The true story was adapted into a movie in 1968, titled The Boston Strangler.

6. Zodiac Killer

Like the BTK killer, the Zodiac (a name he gave himself) killer used a symbol resembling a circle with a cross at the end of his letters to newspapers telling them that he was responsible for at least five murders, maybe more. The killer left behind plenty of evidence; descriptions, calling cards, and fingerprints to name a few, but was never caught. The murders stopped in 1974, and we haven't seen that symbol on a victim since.

The mystery behind this symbol was the fact that there was never an explanation given by the killer. There are plenty of theories, but nothing solid. It could have been something he thought looked like a good signature, or it could mean something way, way more important. We'll probably never know!

5. Beltway Snipers

John Allen Muhammad and Lee Boyd Malvon killed 10 people in Washington, D.C., in October 2002 by shooting them from a distance with their rifles. They had started in February of that year, totaling 17 murders and 10 injuries. The calling card at some of the murders were #tarotcards.

One card was the "Death Card" and had the words “Call me God” written on it for police.

4. Smiley Face Killer

This one sounds like a really bad horror movie. This killer (or killers) are connected to more than 40 deaths of college-age men all over the country that have been made to look like accidental drownings. Using GPS devices and good investigative work, two detectives tracked the flow of the river from the point where each body was found and determined approximately where the bodies were dumped. Around some of the locations, a smiley face was painted on a tree or rock, or some other surface. Each face they found was more haunting than the last. The worst was in Iowa, drawn in red with devil's horns, and the words “Evil Happy Smiley Face Man” written next to it.

The fact that the deaths took place in multiple states, some on the same day, led the detectives to believe more than one killer was involved.

3. Happy Face Killer

What's the deal with these psychos killing the happy face's image? Keith Hunter Jesperson was the original smiley face-drawing serial killer, combining BTK's love of using a signature on his letters to the media, and the #SmileyFaceKiller's love of the smiley face. Jesperson killed 8 women over the course of 5 years, and ended up turning himself in. Oddly, two people confessed to his first murder, and he hated all the attention they got. So, he kept on going. That first murder, which (according to Jesperson) didn't really happen as planned, he took a woman home. Afraid he would go to jail for hitting her, he figured he would just kill her to cover it up. After the other two people got the attention for the murder, he drew his first smiley face on a truck stop (he was a truck driver) bathroom wall, along with an anonymous confession to the murder.

Learn more about Jesperson in the documentary, Keith Hunter Jesperson: The Happy Face Killer.

2. Night Stalker

In just two years, Richard Ramirez killed over a dozen people, and raped and tortured more than 25 others. One of his calling cards was his method of killing; if his intended victims were a couple, he would kill the husband first, and then viciously assault and stab the wife to death. One of his victims had their eyes gouged out. Eventually, thanks to ruthless media and police pressure, Ramirez moved to San Francisco, where he started up his murder spree, losing his Valley Intruder name and gaining the more famous #NightStalker moniker. One of his signatures, thanks to his love of satanic rituals, was to draw a pentagram at some of the crime scenes with the victim's lipstick.

On at least two occurrences, he drew a red pentagram on the thigh of his victim and on a wall in their house. He even drew a pentagram on the hood of his stolen Toyota after getting pulled over for running a red light. The cop tried to chase him, but soon realized he had just let a serial killer get away.

1. Jack the Ripper

Probably the most famous of all serial killers, #JacktheRipper is responsible for at least five murders, but most likely committed many, many more. Stabbing, slashing, cutting, disemboweling are all trademarks of Jack the Ripper's victims. His signature was just that; the gruesome way his victims were found. A more literal signature was on a letter that was supposedly written by the killer himself and was addressed to the police.

If it was him who wrote the letter, then despite how psychotic he may have seemed, he was a little polite. He signed the letter, “yours truly, Jack the Ripper.”

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Who's your favorite serial killer? Tell me on Twitter, right after you ask yourself, "Why in the hell do I have a favorite serial killer?"